1. Field of the Invention
This invention concerns a pump which is especially useful for pumping liquids having abrasive materials as a component thereof, and more particularly to a pump which includes two impellers and two intakes, whereby the primary intake receives liquids containing an abrasive material and a secondary intake receives a relatively abrasive-free liquid for circulation to the primary intake to reduce wear on the pump components and help prevent line plugging.
2. Description of the Prior Art
One of the most commonly encountered problems in dredging operations is the wear on the equipment, particularly the pump. At some dredging sites, the sediment or mineral deposit is relatively soft, and thus the abrasive effect of the particulate in the pumped liquid occurs over a greater period of time, while in other environments, such as coral sand, the abrasive effect renders the pump inoperative in only a few hours. Each time the pump must be shut down and repaired or replaced is lost time to the operator and lost income, and lost dredging time once in position represents one of the greatest sources of lost income to operators.
Another problem encountered by pump operators involves choking of the pump by excessive quantities of pumped material accumulating in the pump or in the discharge conduit. The pumps ordinarily employed in dredging operations are submersible and operate in the immediate vicinity of the sand or other material deposit. The material is conventionally pumped to a floating platform and then off to a disposal site. It is to understood that the greater the ratio of sand or other deposit in the discharge flow, the more efficient and thus more profitable the operation. Unfortunately, the pump may be unable to maintain a positive flow if the intake is momentarily blocked when solids have accumulated in the discharge conduit. The weight of the choked discharge conduit may not only cause a shutdown of the dredging operation, but may necessitate abandonment of the discharge conduit.
The approach of pump manufacturers toward the problems of wear due to abrasion have largely focused on building bigger and thus heavier and more expensive pumps. By reinforcing the pump with a greater quantity of material, a longer useful life may be achieved provided that the operator is willing to pay a greater initial cost and for increased horsepower costs to run the heavier equipment. Another approach has been the use of jet pumps which require a great deal of energy to operate. A third solution has been to employ abrasion resistant liners which are subject to the same abrasion as unlined pumps. A fourth approach is exemplified by U.S. Pat. No. 4,872,809 to Addie et al. wherein the specific dimensions of various parts of the pump are controlled.
Each of these different approaches has achieved an increase in the operating life expected of a pump used in pumping abrasive slurries of sand and the like by recognizing that wear will occur and compensating for the abrasive contact between the abrasive material and the pump components. However, there remains a need for a wear resistant pump which remains highly efficient and achieves an even longer life by protecting the components from the abrasive effects of the pumped material rather than treating the symptoms. There also remains a need for a pump which can maintain a flow in a dredging system even when the intake becomes temporarily choked. These objects include maintaining an efficient output from the pump and the ability to use the pump with existing dredging equipment.